1. Field of the Invention
This invention relates to a press mechanism to drive a press plate, a clamp mechanism of a molding machine which drives one die toward another die, and a molding machine comprising this clamp mechanism.
2. Description of the Related Art
In a press mechanism or a clamp mechanism of a molding machine, a toggle mechanism using, for example, a lever has heretofore been used as a mechanism to drive a press plate (refer to, for example, FIG. 5, description of U.S. Pat. No. 3,159,450). The toggle mechanism urges the press plate to produce torque at its bottom dead center. The toggle mechanism is suitable for the press mechanism and the clamp mechanism of the molding machine because the toggle mechanism can stably produce great pressure and can move the press plate with a great stroke.
Furthermore, as a clamp mechanism for the molding machine, a mechanical device utilizing leverage is known, and this mechanical device uses a drive force from two drive sources to clamp the press plate in two stages (refer to, for example, FIG. 1 to FIG. 4, description of U.S. Pat. No. 3,159,450). This mechanical device is configured in such a manner that an action point is provided at one end of a lever member, a supporting point (or a force point) is provided at the other end, a force point (or a supporting point) is provided in between and the press plate is coupled to the action point. In operating this mechanical device, the force point is first urged so that the lever member pivots on the supporting point, and then with the force point as the supporting point, the supporting point is urged so that the lever member pivots on the force point.
Furthermore, there is leverage in which a supporting point is provided at one end of a lever member, a force point is provided at the other end, an action point is provided in between and a press plate is coupled to this action point (refer to, for example, FIG. 3, description of U.S. Pat. No. 2,703,097). This leverage urges the force point so that the lever member pivots on the supporting point to drive the press plate.
The toggle device shown in FIG. 5 of the description of U.S. Pat. No. 3,159,450 mentioned above can produce comparatively great torque and can have a great moving stroke of the press plate, but its problem is that the position and pressure of the press plate cannot be controlled with high accuracy in the vicinity of the bottom dead center.
Furthermore, the problem of the two-stage driving leverage shown in FIG. 1 to FIG. 4 of the description of U.S. Pat. No. 3,159,450 is that, because the action point to act on the press plate is provided closer to one end of the lever member, torsional stress functions when the two drive sources are used to urge the press plate such that highly accurate parallelism of the press plate cannot be maintained.
Still further, in the leverage shown in FIG. 3 of the description of U.S. Pat. No. 2,703,097 mentioned above, the moving stroke of the action point is smaller than the moving stroke of the force point, so that when the press plate is to be moved with a great stroke, the force point needs to be moved more greatly. With such large movement of the force point, the lever member pivots greatly, and undesirable stress acts on the lever member along its longitudinal direction, thus making it impossible to maintain the highly accurate parallelism of the press plate.
Further yet, in this leverage, one drive source urges the force point to pivot the lever member, so that if a drive source is used which is suitable for moving the press plate with a great stroke, the position and pressure of the press plate cannot be controlled with high accuracy.